1. Field of the Invention
This invention relates to a method of and apparatus for coating a continuous heated substrate, e.g., a glass ribbon.
2. Discussion of the Technical Problems
Pyrolytic oxide coating of a continuous glass ribbon has been recognized in the prior art. For example, in U.S. Pat. Nos. 3,660,061 and 3,850,679; in U.S. patent application Ser. No. 315,394 filed on Dec. 15, 1972, in the name of Krishna Simhan and entitled "Nozzle for Chemical Vapor Deposition", now U.S. Pat. No. 3,888,649, and in U.S. Pat. application Ser. No. 533,609 and 533,610 filed Dec. 17, 1974, in the name of John F. Sopko and entitled "Coating Composition Vaporizer" there is taught a method of and apparatus for coating a continuous glass ribbon as it advances from the exit end of a forming chamber into an annealing lehr.
In general, a coating apparatus is provided in a coating chamber located downstream of the exit end of the forming chamber and upstream of the entrance end of the annealing lehr. The coating apparatus directs a coating fluid, e.g., a heated coating vapor or a coating spray of an organo metallic composition toward the heated glass ribbon and the heat of the glass ribbon pyrolyzes the coating to form a metal oxide coating thereon. Exhaust hoods are provided about the coating apparatus to prevent coating vapors from moving into the annealing lehr and forming chamber.
Although the coating apparatuses taught in the above-mentioned U.S. patents and U.S. patent applications are ideally suitable for applying a pyrolytic oxide coating to the glass ribbon surface, there are other associated problems.
The glass ribbon as it advances from the forming chamber through the coating chamber loses heat by radiation, conduction and/or convection. It has been determined that temperature drops between the exit end of the forming chamber and the entrance end of the annealing lehr can vary between about 100.degree. F. -200.degree. F. (55.degree. C. -111.degree. C.) depending on the type of coating apparatus used, speed of the ribbon and ribbon thickness.
As can be appreciated by those skilled in the art of pyrolytic oxide coating, a glass ribbon temperature variation range of 100.degree. F. -200.degree. F. (55.degree. C. -111.degree. C.) is not acceptable for a uniform and/or durable coating.
Another limitation in the prior art technique of pyrolytic oxide coating is ribbon warpage. Glass ribbons, particularly glass ribbons having a thickness of 1/4 inch (0.64 centimeter) or less, have been found to warp immediately downstream of the coating apparatus. The warpage has a sinuous shape about an axis transverse to the glass ribbon path and amplitudes of up to 3 inches (7.62 centimeters) for glass thickness of about 1/8 inch (0.32 centimeter). With accentuated warpage the downstream exhaust hood and in certain instances the coating apparatus has to be raised to prevent contact with glass ribbon that could mar or fracture the glass ribbon.
An undesirable condition exists when the exhaust hoods are raised greater than about 3 inches (8 centimeters) above the glass ribbon path. For example, the coating vapors are not exhausted and pass into the environment, annealing lehr and float forming chamber. Further, in most instances, a coating inspection device is mounted immediately upstream of the annealing lehr. The coating vapors that are not exhausted deposit on the inspection device rendering it unable to immediately determine the quality of the coating on the glass ribbon.
It would be advantageous, therefore, if the limitations of the prior art pyrolytic oxide coating process were eliminated.